Secret Passage in Magatia

In Magatia, there is a secret passage leading from Alcadno to Zenumist. But, every time I try to enter, it just says "you are not authorized to enter the secret passage."
Can someone please tell me how to get in?

Talk to Parwen the "undead alchemist" to start the quest to gain access to the hidden passage.
He's found in a hidden map connected to the map, "Alcadno Research Institute: Lab - Area C-2".
The hidden portal to his map is on top of a tall pillar-like object with a ladder on it.

Talk to Parwen the "undead alchemist" to start the quest to gain access to the hidden passage.
He's found in a hidden map connected to the map, "Alcadno Research Institute: Lab - Area C-2".
The hidden portal to his map is on top of a tall pillar-like object with a ladder on it.[/quote]